Hi,
Here's my procedure for S1818 (should be very similar for S1813):
Pre-Rinse(preferably with ultrasonics) the sample in : Acetone,
Methanol, and IPA.
Pre-heat the sample at 115C for about 5 minutes to get rid of adsorbed
moisture and solvent and allow to cool down for 10-20 seconds.
Spin: 20s @ 4000rpm, with 4000 rpm/s acceleration (it does make a
difference) the wafer is very small so no "pre-spin" is necessary in
my case. Also, for S18xx series resists HDMS coating appears
unnecessary (I tested tested on Si an GaAs surfaces)
Bake: 1 min at 115C (hotplate top). 3 minutes seem a bit much and
might overbake the resist.
Expose: 12s @ 7.5 mW/cm^2. I also always remove edge beads by exposing
the edges for about 5 minutes and developing before the pattern
exposure(even for S1805 edge beads can be substantial, but it also has
to do with very small size of my sample - ~ 5x5mm).
Develop: 20s MF319 (up to 30s is ok).
For the best adhesion also follow with a short plasma ash , to remove
any underdeveloped resist (the meaning of "short" depends on your
asher).
With this procedure any film can be removed after no more than 10 min
in the ultrasonic bath.
Very importantly, acetone does not appear to be very good for lifting
off S18xx resists, previously I had poor results with acetone. Using
1165 resist stripper improves the process dramatically. Note that
1165 does not dissolve in acetone, so its best to rinse the sample
with DI water and then IPA after exposure to 1165.
I also found that if the sputtering machine exposes targets to air
during sample loading, Ti has to be pre-sputtered for a very long time
(longer than the deposition time) otherwise it will peel off during
lift-off.
hope this helps,
-Mikas
On Tue, Jul 14, 2009 at 1:08 PM, ANIRBAN SARKAR wrote:
> Hey Mikas,
>
> I am a follower of this MEMS forum and I would be interested to know about a
> little bit more in regards to to S18XX processing and S1818 processing which
> you have mentioned in your post.
>
> Recently I am doing lift off with S1813 and my processing is failing
> everytime over the past few weeks.
>
> Here is my process conditions with S1813.
>
> Substrate: silicon nitride on Si
> Spin coating: HMDS for proper adhesion
> for S1813 500 rpm for 10 secs, 1000 rpm for 1000 secs,
> 1800 rpm for 15 secs
> the thickness in the alpha step shows around 1.3 microns
> Pre baking time: 110'c for 3 mins
> Exposure: Intensity is 10mW/cm2 Time; 15 secs for a total dose of
> 150mJ/cm2**
> development: MF 319 for 30 secs
> Smallest feature size: 10 ums
>
> Physical vapor deposition: Sputtering
> Ti about 60nm
> Cu about 200nm
>
> The sample is then placed under Acetone ultrasonics for 1 hr for lift off..
> ** the contact of the mask with the sample is extremely good since S1813
> hardly gives you any edge bead and the exposure is done in contact.
>
> But unfortunately the process is failing since either most of the patterns
> are peeled away after lift off or are poorly lifted off which chunks of
> metal still remaining in the sample.
>
> I will be interested to know about any suggestions for the above processing.
> Further, it will be nice if you can let us know about the routine procedure
> of S1818 that you follow for lift off.
>
> Thanks a lot
> Anirban